Cracking hydrocarbon oils



Sept. 12, 1944. P. OSTERGAARD 2,358,184

CRACKING HYDROCARBON OILS Filed July 26,;940 v 2 sheets-sheet 1 ...lill Pill.

NW. WWA ...HIIIIIIIIU Nimm WNY i SePf- 12, 1944- P. OSTERGAARD CRACKING HYDROCARBON OILS 2 Sheets-Sheet 2 Filed July 26, 1940 ADD @m6, Wm.

POI/ s/ergaard All P0 t I Patented Sept. 12, 1944 UNITED STATES PATENT OFFICE CRACKING HYDRO CARBON OILS Application July 26, 1940, Serial No. 347,737

(ci. 19e-9i 3 Claims.

My invention relates to cracking hydrocarbon oils, and more particularly the manufacture of light hydrocarbon oils useful as motor fuels and of high antiknock value when so used, and having especial utility for use as aviation fuels.

My invention is especially applicable to the production of motor fuels, including gasolines and safety fuels, and an object achieved by my invention is the production of such fuels in higher yields and of higher antiknock values than are possible with prior thermal cracking methods.

In my prior Patent No. 2,135,014, I have disclosed a process of cracking hydrocarbon oil in which gaseous hydrocarbons having 3 to 4 atoms per molecule are delivered to the oil cracking zone, and the conversion of the admixed oil and gases is carried out under conditions effective to obtain a high degree of conversion per pass, thereby resulting in improvements in both the yield and antiknock value of the gasoline distillate produced. The process of my aforesaid patent makes it possible to achieve very substantial improvement in both of the factors noted, but, as in all processes, there are inevitable limits with respect to the maximum yields and antiknock values of the gasoline products obtained.

My present invention comprises certain specific improvements, preferably conducted within the scope of the process generically claimed in my aforesaid Patent No. 2,135,014, whereby it is possible to produce light hydrocarbon fuels having extremely high antiknock values, and particularly suitable for use as aviation fuels.

In accordance with my present invention, hydrocarbon oil is subjected to cracking, preferably in gas dilution, the products of conversion are fractionated to recover a liquid fraction comprising a light cracked distillate including cracked gasoline constituents as well as all or a major portion of those products of conversion which contain 4 carbon atoms per molecule (butanes and butylenes). The aforesaid fraction is then subjected to conversion in a separate conversion zone or cracking coil, and the products are fract'onated to recover a motor fuel fraction therefrom; the latter fraction being treated and refractionated as desired or necessary to produce motor fuel products of the desired specifications.

My present invention further comprises a procrss in which cracked hydrocarbon distillate, produced in an initial cracking zone, is subjected to further conversion in a second and separate conversion zone, in the presence of normally gaseous constituents containing 4 carbon atoms per molecule produced in the initial conversion zone.

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By diverting these normally gaseous constituents from the first conversion and fractionating zone into the second conversion and fractionating zone into the second conversion zone, the re-cracking of the cracked normally liquid distillate produced in the first zone is enchanced, the normally gaseous constituents are converted into high octanenumber gasoline, and degradation of the gasoline-like hydrocarbons produced from the normally gaseous constituents is prevented.

In a specific and preferred embodiment of my invention a hydrocarbon oil, such for example as a naphtha. kerosene, a furnace oil or a light gas oil, is subjected to cracking in an initial conversion zone, in the presence of normally gaseous hydrocarbons containing from 2 to 3 carbon atoms per molecule. The products of conversion are fractionated to recover a distillate fraction comprising both normally liquid gasoline-like hydrocarbons and normally gaseous constituents containing 3 to 4 carbon atoms per molecule, and this fraction is subjected to further conversion in a second and separate conversion zone. The products of conversion from the second conversion zone are fractionated to recover a motor fuel distillate therefrom, which may be treated and re-run as aforesaid, while normally gaseous hydrocarbons produced in the second conversion zone are returned to the fractionating zone receiving the products from the first-mentioned conversion zone. In this particular embodiment of my invention it will be observed that all normally gaseous products from both zones are eventually handled in a single fractionating system. The operation of the unit is so carried out as to avoid the return of any substantial portion of the normally gaseous constituents containing 4 carbon atoms per molecule to the initial convesion zone; these being delivered to the second conversion zone. With respect to the normally gaseous constituents containing 2 to 3 carbon atoms per molecule, produced in both zones, these are delivered in part to the initial cracking zone, as for example by absorption in the charging liquid stock about to be delivered to the initial conversion zone. A considerable portion of the normally gaseous hydrocarbons containing 3 carbon atoms per molecule, over and above that portion recirculated to the initial conversion zone, is delivered to the second conversion zone.

Thus it will be observed that in this particular embodiment, the oil cracking in both of the conversion operations referred to is conducted in gas dilution. Some conversion of the gases undoubtedly takes place in the initial conversion zone, as well as in the second conversion zone. In the rst conversion zone, however, the primary purpose of introducing normally gaseous hydrocarbons containing 2 to 3 carbon atoms per molecule is to enhance the cracking of the oil. In the second conversion zone this object also obtains, but a more thorough degree of conversion of the normally gaseous hydrocarbons present in this zone is effected.

Both of the conversions referred to are effected under super-atmospheric pressure and temperature. The temperatures will, of course, depend upon the character of the charging stocks, but in general will range from 950 to 1250o F. while pressures from 500 to 3000 pounds per square inch are suitable. In each conversion zone, however, optimum results are obtained by operating at temperatures which, with respect to the individual charging stock, are within the invention set forth and claimed in my prior Patent No. 2,135,014. In other words, the conversion in each zone is carried out at a temperature and at a degree of conversion per pass higher than could be employed or effected in the absence of the normally gaseous hydrocarbons, without serious carbon deposition.

In a further embodiment of my invention, a third conversion zone is employed. The charging stock for this zone is obtained by recovering from the products in the second conversion zone referred to above a fraction intermediate between the heaviest products and the gasoline or motor fuel fraction. This fraction is subjected to further cracking in a third conversion zone, preferably in admixture with normally gaseous hydrocarbons containing from 3 to 4 carbon atoms per molecule, derived elsewhere in the system, and the products are combined with the products of conversion from the second conversion zone for subsequent fractionation and recovery.

In order that my invention may be more fully set forth and understood, I now describe, with reference to the drawings accompanying and forming part of this specification, various preferred forms and manners in which my invention may be practiced and embodied. In these drawings,

Fig. 1 is a. more or less diagrammatic elevational view of apparatus for carrying out my process in one embodiment thereof, and

Fig. 2 is a similar view of somewhat modified apparatus for carrying out a further variation of my process.

Similar reference numerals designate similar parts in both views of the drawings.

Referring now to the operation illustrated in Fig. 1, a suitable charging stock, such as a naphtha or gasoline, a kerosene or a light furnace oil stock, is introduced into the system through a line I and is delivered by a pump 2 through a line 3 into the upper portion of an absorber 4. Absorber 4 receives cracked gases (produced as set forth hereinbelow) through a line 5 which terminates in the lower part of the absorber 4.

As the charging stock flows downward through the absorber 4 it absorbs from the gases also traversing the absorber 4 constituents containing 2 and 3 carbon atoms per molecule. The residual gases, comprising mainly hydrogen, methane. ethane and ethylene but which may also contain small amounts of propane and propylene, are removed from the top of the absorber 4 through a line 6 wherein is located a pressure-controlling valve 1 of conventional type, adapted to maintain a suitable pressure within the system.

The enriched charging stock, containing absorbed normally gaseous hydrocarbons, is removed from the bottom of absorber 4 through a line 8 wherein is located a pump 9 and a. heat exchanger I0, the latter serving to preheat the enriched charging stock. After passing through the heat exchanger III, the enriched charging stock continues through the line 8 into and through a cracking coil I2 suitably disposed within a cracking furnace I3. By means of heat suitably applied in the furnace I3, the enriched charging stock is subjected to a high cracking temperature ranging from about 950 to 1250n F., under a back pressure from 500 to 300 pounds per square inch, for a suficient time to effect substantial conversion of the charging stock, cracked gasoline and gases.

As pointed out hereinabove, the conversion effected in the coil I2 preferably takes place at a higher temperature and at a higher degree of conversion per pass than could be attained, under otherwise similar conditions and without serious carbon deposition, in the absence of the normally gaseous hydrocarbons picked up by the charging stock in the absorber 4. Due to the gas dilution, it is possible to effect the conversion of the initial charging stock in such manner as to obtain a relatively high yield of low boiling constituents, including gasoline hydrocarbons and normally gaseous constituents.

Some conversion of the normally gaseous constituents contained in the enriched charging stock delivered to the coil I2 is also effected, particularly with respect to those normally gaseous constituents (propane and propylene) containing 3 carbon atoms per molecule; to some extent, these normally gaseous constituents are converted to gasoline-like hydrocarbons of high antiknock value, by cracking, polymerization, alkylation, or a combination of these types of conversion reactions.

The hot products of conversion leave the coil I2, passing through a transfer line I4, wherein is located a pressure-reducing valve I5, into the lower part of a combined evaporator-fractionator I6, of more or less conventional type. During their passage through the transfer line I4, the products of conversion from the coil I2 are cooled (quenched) to a temperature below a temperature at which further conversion reactions would proceed, by the introduction of relatively cool oil delivered into the transfer line I4 through quench line I1. While cool oil from various sources may be used for this purpose, that employed in the instance illustrated in Fig. 1 is derived elsewhere in the system, in a manner to be described hereinbelow.

Suitable means are provided for cooling the various products traversing the evaporator-fractionator I6. Various means may be employed for this purpose, but in the instance illustrated a side stream is withdrawn near the upper part of the tower I6 through a line 20. This stream is first caused to give up a portion of its sensible heat to the fresh charging stock by traversing the indirect heat exchanger I0 and is then passed through a cooler 2| Where its temperature may be reduced to a still lower point. Upon leaving the cooler 2| the stream of oil passes through a line 22 to a pump 23 whence it is returned through a line 24 to the upper portion of tower I2, thereby serving as a cooling and reiluxlng medium.

In the tower I6, by virtue of the cooling and pressure reduction, constituents boiling above a naphtha end boiling point, for example constitu-4 ents boiling above about 400 F., are separated and condensed. The condensate, comprising mainly gas oil and heavier constituents, is drawn from the bottom of tower I6 through a line 25 for further disposition, as setforth further hereinbelow.

The remaining vapors and gases leave the top of tower I6 through a line 26 which, as shown, may be provided with a cooler 21, and are then delivered to a fractionating column 28 of a more or less conventional design. Column 28 is provided with means including a line 29 for cooling and reiiuxing the upper part of the column and with means for Lsupplying heat to the lower portion of the column; the last mentioned means comprising, in the instance shown, a reboiler 30 which communicates with the lower part of column 28 through a condensate line 3| and a vaporreturn line 32.

Uncondensed gases leave the top of the fractionating column 28 through a line 33, wherein is located a cooler 34, and pass to a separator 35. Condensate collected in the separator 35 is returned by means of a line 36. a pump 31 and the line 29 to the upper part of the column 28, as a cooling and refiuxing medium.

The operation of the fractionating column 28 is so conducted as to eiect the condensation of a fraction containing not only gasoline or naphtha constituents but also constituents containing 4 carbon atoms per molecule (butanes and butylenes). In the preferred operation, all or substantially all of the last mentioned normally gaseous constituents in the conversion products from the coil I 2 are caused to be condensed in the distillate fraction removed from the column 28. A portion of the normally gaseous hydrocarbons containing 3 carbon atoms per molecule may also be condensed and similarly withdrawn in this fraction. The condensate passes through the line 3|, through the reboiler 38 and thence through a line 38 to a pump 39, to be utilized in the manner shown hereinbelow The gases removed from the upper part of the separator 35 comprises hydrogen, methane, ethane. ethylene, propane and propylene, and may also contain minor quantities of higher boiling constituents, although the amount of the latter should be kept as low as possible if the best results are to be secured. These gases pass through a line 4I and then line 5 into the absorber 4, where they are scrubbed Ywith fresh charging stock in the manner set forth hereinabove.

The cracked distillate fraction recovered in the column 28. comprising naphtha or gasoline-like constituents and constituents containing from 3 to 4 carbon atoms per molecule, is delivered by means of the carbon atoms per molecule, is delivered by means of the pump 39 through a line 42 wherein is located a heat exchanger 43 to a second conversion coil 44 located within a suitable cracking furnace 45. It will be readily understood by those skilled in the art. that the coil 44 may be located in the same furnace as the coil I 2, wherever this is desirable.

In traversing the coil 44, the normally liquid and normally gaseous hydrocarbons contained in the fraction removed from the column 28 are subjected to a high cracking temperature under a high pressure, for a suicient time to obtain optimum conversion of the normally liquid and normally gaseous hydrocarbons to products within a motor fuel boiling point range and of high antiknock value. In general, the ranges of temperatures and pressures employed in coil 44 are similar to the ranges of temperatures and pressures employed in coil I2, that is to say, the ternperatures will run from 950 to 1250" F'. and the pressures from 500 to 3000 pounds per square inch. In some instances it may be possible to carry somewhat higher temperatures and pressures in the coil 44 than are carried in coil I2. In general, however, similar temperatures and pressures will be employed in each coil, but it is pref'- erable to so design the coil 44 as to provide for a longer soaking time than is provided for in the coil I2. As in the previous instance, optimum results are obtained when the temperatures and the degree of conversion per pass are maintained at higher levels than could be maintained, under otherwise similar conditions, in the absence of the normally gaseous hydrocarbons and without such deposition of carbon as to interfere with the operation of the unit within a comparatively short time. In short. the best results are obtained when operating in accordance with the method of operation generically set forth and claimed in my prior Patent No. 2,135,014.

The hot products of conversion leaving the coil 44 through a transfer line 46 are first quenched to a temperature below active conversion temperature by means of relatively cool oil introduced through a quenching line 41, and then pass through a pressure-reducing valve 48 into an evaporator-fractionator 49 of more or less conventional designl It is advantageous also to deliver into the tower 49 the relatively high-boiling products removed from the bottom of the tower I6 through the line 25. In the instance illustrated, this is accomplished by means of a pump 5| and a line 52 communicating with the transfer line 46.

As in the case of the tower I6, the tower 49 is provided with suitable cooling and refluxing means. In the instance illustrated in Fig. 1, such means comprise a line 53 adapted to remove a side stream from the upper portion of the tower 49, as well as the heat exchanger 43, a cooler 54, a pump 55 and a reflux line 56. The side stream withdrawn from the tower 49, after being cooled in the heat exchanger 43 and still further cooled in the cooler 54 is returned to the upper part of the tower 49 through the line 56.

In the tower 49, by virtue of pressure reduction, cooling and refiuxing, relatively high-boiling constituents, having a boiling point range higher than is desired in the final motor-fuel product, and comprising mainly gas oil and tarry constituents. are caused to be separated in liquid form. The fraction so separated is withdrawn from the bottom of the tower 49 through the line 51. A portion of this fraction is employed as a quenching medium in the system. this portion passing through a line 58, reboiler 59, a line 60, the reboiler 30, a line 62, a cooler 63 and a line 64, wherein is located a pump 65. The pump 65 in turn delivers suitable portions of this oil, through lines I1 and 41. to the transfer lines I4 and 46, respectively. Suitable valves (not shown) may be provided in the lines I1 and 41 for controlling the proportions delivered to the transfer lines I4 and 46, respectively.

After the unit is in full operation. that portion of the residuum or tar withdrawn from the tower 49 which is not required for cooling purposes in the system is withdrawn from the system through a line 66, and is disposed of as desired.

The gases and vapors leaving the top of the,

tower 49 pass through a vapor line 10, where'in may conveniently -be located a cooler 1I, into a fractionating column 12 which, as in the case of the column 28, is of more or less conventional design. Heat is supplied to the bottom of the column 12 through the reboiler 59 which communicates wtih the base of the column 12 through a distillate line 13 and a vapor return line 14. Suitable means are also provided for cooling and refiuxing the upper part of the column 12; such means, in the instance illustrated in Fig. 1, comprising a reux line 15.

The operation of the fractionating column 12 is so conducted as to eiect the condensation and removal of a stabilized motor-fuel fraction comprising mainly gasoline-like constituents, as well as somewhat heavier constituents within a safety-fuel boiling point range. This stabilized motor-fuel fraction or cracked distillate, after leaving the reboiler 59 passes through a line 16, wherein may be conveniently located a cooler 11, and is Withdrawn from the conversion system. As shown in Fig. l, this cracked distillate may be delivered to a unit 11 where it is refined by suitable means, as for example treatment with sulfuric acid at low temperatures, to remove undesirable, unstable constituents. Various other types of treating processes may be employed, such processes and their purposes being well known in the art.

After treatment in the treating unit 11', the distillate may be subjected to further distillation or re-running in order to secure a fraction or fractions of the desired boiling point range. This is accomplished, in the instance shown in Fig. 1, by delivering the treating distillate by a line 18 to a re-run unit 19, wherein the oil is distilled to recover (l) an aviation gasoline, that is to say a gasoline having an end point of around 300 to 310 F., (2) a safety fuel boiling for exexarnple between 300 and 430 F., and (3) a heavy polymer fraction comprising those constituents (either contained in the initial distillate fraction r produced in the treating operation) the boiling points of which are too high to permit their inclusion in a motor-fuel product suitable for use in internal combustion engines of the usual type. In the instance illustrated in Fig. 1, these three fractions are removed from the system through lines 80, 8| and 82, respectively.

The gases remaining uncondensed after the condensation and stabilization effected in the column 12 pass through a line 90 and a cooler or condenser 9| into a separating drum 92. The condensate collecting in the drum 92 is withdrawn by a line 93, wherein is located a pump 94. In the instance illustrated in Fig. 1, a portion of this condensate is returned to the column 12 through the line 15, as a cooling and reuxing medium. The remaining portion of this condensate, comprising mainly hydrocarbons containing 4 carbon atoms per molecule, is returned to the fractionating system provided for the purpose of collecting the products of conversion produced in the coil I2. This may be variously accomplished, but in the instance illustrated, such return is advantageously effected by delivering this portion of the condensate from the separator 92 through the lines 93 and 94 into the upper portion of the column 29 as a cooling and reuxing medium. Normally gaseous hydrocarbons having 4 carbon atoms per molecule, contained in the distillate so returned, are picked up in the fraction condensed in the column 28 and are eventually returned to the cracking coil 44 for further conversion.

Normally gaseous hydrocarbons containing 2 and 3 carbon atoms per molecule, as well as such hydrogen and methane as may be contained in the products of conversion produced in the coil 44, leave the top of the separator 92 in gaseous form and are advantageously delivered through a line 95 and the line 5 into the absorber 4, wherein they are subjected to absorption in the manner hereinabove set forth.

In the preferred operation of the entire system, illustrated in Fig. 1, all or substantially all of the butanes and butylenes produced in the system are eventually returned to the cracking coil 44 for conversion. Those hydrocarbons containing 3 carbon atoms per molecule, also produced in the system, are returned in part to the coil I2 and the coil 44, except in instances where it is desired to return them as completely as possible to the cracking coil I2 or the cracking coil 44.

A variable proportion of the hydrocarbons containing 2 carbon atoms per molecule, produced in the entire system, is returned to the coil I2; for best results it is usually desirable to avoid returning any of these constituents to the coil 44, although my invention does not necessarily exclude the return of such constituents to the coil 44. Operating in this manner, the conversion of 4 carbon atoms to gasoline-like carbon atoms or polymers is largely confined to the coil 44. When such conversion is effected in coil I2 to any extent, the polymer gasoline thereby formed and having an extraordinarily high antiknock value would only be degraded, and the yield thereof reduced, by further conversion in the mold 44. In the coil I2, however, the C2 and C3 hydrocarbons permit the maintenance of drastic cracking conditions, by virtue of the gas-dilution effect thereby secured. The operation constitutes a distinct improvement over operations of a similar character conducted in a single coil and under operations in which the gases and the oil are subjected to conversion in separate units. Subjecton of the initial charging stock to successive cracking in the coils I2 and 44 has the advantage that tar produced in the original cracking operation is removed prior to the entry of the remaining liquid products of conversion into the second cracking Zone. As in other cracking operations, the extent to which the conversion per pass can be pushed in the two coils is limited by formation of tar and the subsequent reduction of the tar to carbon. However, in the operation described, the extent of conversion can be pushed to obtain simultaneous improvements in octane number and yield, over levels impossible to attain in previous types of operation.

In some instances it may be desirable to confine the product of the unit to an aviation gasoline, and to operating in such a manner as not to produce a safety-fuel fraction, but on the contrary to convert constituents which would normally fall within a safety-fuel boiling point range into relatively lower-boiling aviation-gasoline constituents. This may be readily accomplished, in accordance with my invention, by means of the apparatus and process illustrated in Fig. 2. In this instance, operation of the towers 49 and 12 is varied by withdrawing aside stream from the tower 49, of such character as to contain most, or all of those constituents which would otherwise comprise a safety-fuel fraction, that is to say constituents boiling between about 300 and about 430 F. This side stream is withdrawn through a line IOI and is delivered by means of a pump |02 and line |03 to a cracking coil |04 located Within a suitable cracking furnace |05. A portion of the liquid condensate from the separator 92 may also be delivered to the coil |04 by means of a line |06, a pump |01, a line and a line |03, so that the cracking of this oil may proceed in gas dilution, in accordance with the process disclosed and claimed in my prior Patent No. 2,135,014.

Somewhat lower temperatures and pressures may be maintained in the coil |04 than in the coils l2 and 44, for example, temperatures ranging from 900 to about 1150 F. and pressures of from 500 to 1500 pounds per square inch, the precise temperature being of course dependent upon the precise stream withdrawn from the line |0| and the precise character of the normally gaseous hydrocarbons returned through the line |08.

The hot products of conversion leaving the coil |04 are suitably quenched with relatively cool oil through a line |06 supplied by the pump 65 and then pass through a transfer line |01, wherein is located a pressure-reducing valve |08, into the lower part of the evaporator-fractionator 49.

Operating in this manner, constituents which, in the operation illustrated in Fig. 1, would eventually be recovered as safety-fuel, may be subjected to further conversion into relatively lower boiling hydrocarbons, suitable for use as high grade aviation gasoline. That is to say, a product having an end boiling point 0f around 350 F.

In the various conversion coils illustrated in Figs. 1 and 2, the gas dilution will ordinarily vary between 0.5:1 and 5.0:1, stated in terms of the gas: oil ratio on a liquid-volume basis. Where desired, however, additional outside gases may be introduced into the system, and in such cases higher ratios may be employed where desired. 0n the other hand, my invention is also applicable to a process in which oil is cracked in the initial coil without any gas dilution, although this is generally a less desirable type of operation.

The following table will illustrate typical results obtainable in accordance with my invention, operated in accordance with the modication illustrated in Fig. 1:

Charg- Untreated Finished Frsthed ing distillate aviation s ,50'15" stock product gasoline product Yield:

Per ccnt by volume of charging stock.. 100. 0 70.0 27. 4 24. 7 Ier cent by volume of untreated distillate 100. 0 39. 2 35. 3 Inspection:

Gravity, API 47. 5 50. 3 55. 8 36. 2 Sulfur, per cent 0.019 0.011 Acid heat, "F 2 61 l0 2 Aniline point, F.... 136 50. 0 Octane No.-CFR

ASTM 47 82 77 80 +1 cc TEL/gaL. 57 86 84 86 +2 ee TEL/gal.. ss 88 s1 +3 cc TEL/gal.. 66 90 90 88 Distillation:

Over point oF 266 88 114 301 End point, F. 431 495 307 426 10% at, 290 146 15G 311 at, 290 185 170 314 50% at, uF 311 200 205 326 90% at, "F 372 390 250 372 In the operations set forth and described hereinabove with reference to both Figs. 1 and 2, it is usually desirable to transfer as much as possible of the butanes and butylenes produced in the system to coil 44 for conversion; in the operation illustrated in Fig. 2, some of these constituents are also delivered to the coil |04. Ordinarily, the propane and propylene produced in the system are delivered in part to the coil l2 and in part to the coil 44 or to the coils 44 and |04. Ethane and ethylene produced in the system are delivered, at least in part, to the coil l2; these constituents are not ordinarily delivered to the coil 44 or the coil |04.

Where desired, all of the propane and propylene may be delivered to the coils 44 and |04, along with the butanes and butylenes. On the other hand, the operation may be varied by delivering all or substantially all of the propane and propylene to the coil I2.

It will thus be apparent that the systems set forth hereinabove provide for suitable exibility of operation, especially with respect to the distribution and recycling of the various normally gaseous constituents produced in the cracking of the oil.

While, for purposes of illustration, I have described my invention with reference to certain specific embodiments and details, it will be apparent to those skilled in the art that my invention may be variously practiced and embodied, within the scope of the claims hereinafter made.

What I claim is:

l. The process of manufacturing hydrocarbon oil suitable for use as fuel in internal combustion engines, especially aviation engines, and having a high antiknock value when so used, which comprises subjecting hydrocarbon oil to crackinmf/l in a first conversion zone under conditions effective to cause the production of a relatively high yield of gasoline hydrocarbons, recovering from the products of conversion constituents boiling. above a gasoline boiling point range, gasoline constituents, normally gaseous constituents having 4 carbon atoms per molecule, and normally gaseous constituents having from 2 to 3 carbon atoms per molecule, returning the last-mentioned normally gaseous constituents to said first conversion zone in admixture with said oil, simultaneously subjecting said gas`olEivre/constituents and said normally gaseousmconsg uentshling 4 carbenfatns per molecule to cracking in a second conversion zone under conditions effective to cause further conversion of said gasoline constituents to gasoline constituents of higher antiknock value and simultaneous conversion of said normally gaseous constituents to gasoline-like polymers, and recovering the last mentioned gasoline and gasoline-like products from the products of conversion produced in said second conversion zone.

2. The process of manufacturing hydrocarbon oil suitable as fuel in internal combustion engines, and especially aviation engines, and having a high anti-knock value when so used, which comprises subjecting hydrocarbon oil to cracking in a rst conversion zone under conditions effective to cause the production of a relatively high yield of gasoline hydrocarbons; separating from the products of conversion a flrst fraction comprising mainly constituents boiling above the gasoline boiling-point range and a second fraction comprising gasoline constituents and at least a, portion of normally gaseous constituents having four carbon atoms per molecule; subjecting said second fraction to cracking in a second conversion zone under conditions effective to cause further conversion of said gasoline constituents to gasoline constituents of higher anti-knock value and simultaneous conversion of said normally gaseous constituents to gasoline-like polymers; condensing and recovering the last-mentioned gasoline and gasoline-like products; re-

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covering normally gaseous constituents containing three carbon atoms per molecule from the products of conversion produced in the first and second conversion zones; recycling a portion of said last-mentioned normally gaseous constituents to said first conversion zone; and recycling at least a major part of the remaining last-mentioned normally gaseous constituents to said second conversion zone.

3. The process of manufacturing hydrocarbon oil suitable as fuel in internal combustion engines, and especially aviation engines, and having a high anti-knock value when so used, which comprises subjecting hydrocarbon oil to cracking in a first conversion zone under conditions effective to cause the production of a relatively high yield of gasoline hydrocarbons; separating from the products of conversion a rst fraction comprising mainly constituents boiling above the gasoline boiling-point range and a second fraction comprising gasoline constituents and at least a portion of normally gaseous constituents having four carbon atoms per molecule; subjecting said second fraction to cracking in a second conversion zone under conditions effective to cause further conversion of said gasoline constituents to gasoline constituents of higher anti-knock value and simultaneous conversion of said normally gaseous constituents to gasoline-like polymers; condensing and recovering the last-mentioned gasoline and gasoline-like products; combining normally gaseous constituents in the products of conversion from said second conversion zone, after recovery of high-boiling products, with the products of conversion from said rst conversion zone; scrubbing gaseous products of conversion from said first conversion zone remaining after recovery of said second fraction with hydrocarbon oil about to be delivered to said first conversion zone, for the recovery of normally gaseous constituents containing from two to three carbon atoms per molecule; and returning said constituents containing from two to three carbon atoms per molecule to said first conversion zone in admixture with said hydrocarbon oil.

POVL OSTERGAARD.

CERTIFICATE 0F CORRECTION. Patent No. 2,553,18u. september 12, 19141;.

POVL OSTERGAARD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, second column, line 5, strike out the words "into the second conversion and fractionating zone"; page 2, second column, line ILL, for "500 pounds" read --5000 pounds; page 3, first column, lines 59 and 60, strike out "means of the carbon atoms per molecule, is delivered by"; page Lp, first column, line 59, after "for" strike out "ex-"g and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

signed and sealed this mth day of November, A. D. 19h14.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

